Grid leak for radio apparatus



June 14, 1927. 1,632,089

R. E. MARBLE RY GRID LEAK FOR RADIO APPARATUS Filed Jan. 24, 1921 WITNESSES: INVENTOR I g g Ra/p/z E, Narbu/y, I O m. M I I W ATTORNEY Patented June 14, 1927.

A RALPH E. MARBURY, or nnenwoon PARK, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANYQA CORPORATION OF PENNSYL- IVANIA.

GRID LEAK FOR APPARATUS.

Application filed January 24, 1921. Serial No. 439,360..

This invention relates to resistance units, more especially to devices which are particularly adapted for useas grid leaks for radio apparatus and having resistances which vary from about 100,000 ohms to megohms. 7

Resistance units, especially low priced units, for use as grid leaks, are inconsider- L able demand in radio apparatus. Hereto- 'fore, several types of grld leaks were proposed, such units consisting of small strips of fibrous sheet material, usually paper,

' about'one inch long and one-eighth to onequarter inch wide. with various substances having relatively high resistance, such as india drawing ink, and then dried.

"-Since it is rather difiicult to obtain coated materials of this type having uniform resistance, d1t1ons, dividual on account of yarying drying con- 1t was necessary to ZLdJllSt each mto a l/Vheatstone' bridge arrangement and to of the unit was'raised to the desired value.

resistance per unit area.

Since the conductor was composed of a comparatively small number of particles having good conducting properties making loose contact with one another, the unit was relatively unstable, and a slight disturbance of the surface of thematerial resulted in a large change in resistance, often several hundred percent.

My invention is designed to obviate this disadvantage, it being among the objects thereof to device a resistance unit adapted for grid leaks which is simple in construction, and the resistance of which does not change.

In practising my invention, I provide a resistance unit in which the conducting particles are large in number and are connected in parallel. Such an arrangement of particlesmakes the unit stable and also makes it possible to use a material having a high More specifically, I form a resistance unit by providing a thin,

porous sheet of paper with suitable resistance material and strips of foil, in parallel thereof, the outer edges of placing along "tile edges the strip extends ing beyond the edges of the paper, and their inner edges being spaced apart. The assem- The material was coated grid leak {by connecting the same which is impregnated bly is rolled to" form a rod which is then the foil being perterminal connections for Fig. l is a perspective view of the mate.

rial, from Whlch my resistance unitis formed, in the process of being rolled Fig. 2 is a perspective view showing the treatment and the relative positions of the parts; i

Fig. 3 is a plan view of sistance unit, and

,Fig. 4 a side view thereof.

ll provide a mandrel -1 upon which is placed a roll of suitable fibrous sheet material, such as a thin, porous, tissue paper 2. I provide also a mandrel 3 upon whichare mounted two rolls 4 and-5 of foil, generall copper, tin or aluminum, the foils being spaced apart and the outeredges thereof extending an appreciable distance beyond the edges of the sheet 2 of paper. I further provide a tank 6 containing a solution of resistance material, such as a solution of its passage through the tank 6. If desired,

the impregnated sheet material may be passed through a drying tower (not shown) before being rolledupon mandrel 10, the

.iilverbeing precipitated by exposure 'to light efore the sheet. material is rolled on the mandrel. The parallel sheets of foil 4 and 5, the outer edges of which extend beyond the edges of sheet 2, are rolled therewith upon mandrel 10.'

When a suitable number of turns have been rolled on the mandrel, the assembly is cut away, the mandrel remdved and the assembly c onipressed to flatten it, as shown .in Figs. 3 and 4. It is then baked under slight pressure to harden the shellac in the impregnating'mixtureand hold the various laminations together. The final I adjustment of the resistance unit may be made by the completed red placing the same in a Wheatstone bridge arrangement, unwinding the proper number of turns and removing them until the desired resistance is obtained.

By reason of thelarge surface area and the high resistance-per-unit area, thenurnber of turns does not have to be very accurate, and the adjustments made in the lVheatstone bridge will not cause critical changes of resistance. The removal of more or less of the material than is necessary to give a certain final resistance value does not appreciably change the resistance of the entire unit.

After the adjustment is made, the unit is dipped in shellac and baked to harden the same, giving a structure which is protected from the atmosphere and which does not change in resistance when subjected to ex terior disturbances. The unit may be placed in a suitable holder, being held in place by screws 13 and 14: extending through openings 11 and 12 in the flattened ends of the metal toils.

It is obvious that my invention may be practised by various modifications of the method I have above described, and I do not confine myself to the steps enumerated or to the materials used. It is obvious that various forms of resistance units may be made embodying the principles laid down herein.

I claim as my invention 1. A resistance unit comprising a plurality of strips of foil and material having high resistance interposed therebetween and rolled to form a unit. j

2; A resistance unit comprising a rolled sheet of fibrous insulating material and strips of foil placed longitudinally thereof, said strips being separated, said sheet. of insulating material carrying a finely divided conducting material.

3. A resistance unit comprising a rolled sheet of fibrous insulating material and a strip of foil at each edge of said sheet, the outer edges of said foils extending beyond the edges of said sheet and the inner edges thereof being separated, said sheet of insulating material carrying a finely divided conducting material and a binding materiah kt. A resistance unit comprising a rolled sheet of fibrous insulating material, a strip of foil at each edge of said sheet, the outer .said sheet and the inner edges of which are separated, and finely divided metal within said sheet.

6. A resistance unit comprising a rolled sheet'of fibrous insulating material, a. strip of foil at each edge of said sheet, the outer edges of which project beyond the edges of said sheet and the inner'edges of which are separated,'a nd finely dividedsilver within said sheet.

7. A unit'havirig highresistance and comprising a fibrous body having laminar end terminals embedded therein, said fibrous body being impregnated with a finely divided conducting material,

8. A unit having high resistance and comprising a body of composite material and laminar end-terminal conductors embedded therein and separated from each other, said composite material comprising a finely divided conducting material and an insulating material.

In testimony whereof, I' have hereunto subscribed my name this 17th day of J ailuary, 1921.

; RALPH E. MARBURY. 

